On occasion, it is possible for the medium to obscure the message. Tangerine, however, is an example of technique complementing storytelling perfectly. It was filmed entirely on three iPhone 5s, equipped with clip-on anamorphic lenses, handheld Steadicam mounts and a Filmic Pro app.

Admittedly, Tangerine is not the first phone-footage film – forerunners include Olive, shot on a Nokia N8. But it is certainly the best turned out. Colours are surprisingly vibrant, the low-fi cinematography capturing the radiant orange hue of smoggy Los Angeles sunsets. But this is a grubby yarn, where the practicalities and deprivations of street life are given shape through director Sean Baker’s empathic inquisitiveness.

Sin-Dee (Kitana Kiki Rodriguez) is a transgender prostitute who is released from a month in jail only to discover that during her stay inside her pimp and boyfriend Chester (James Ransone) has been unfaithful. Teaming up with her best friend, Alexandra (Mya Taylor), Sin-Dee careens round the scruffy streets of Los Angeles – seemingly forever in the shadow of the Hollywood sign – hunting for Chester and the other woman.

It is a bittersweet film and despite the brash camaraderie between Sin-Dee and Alexandra, shot through with a tinge of melancholia. What life is this for anyone, asks Baker, as he tours one of the city’s most sordid subcultures. But perhaps Tangerine’s greatest success is in the way that we are encouraged to view the dynamic between Sin-Dee and Alexandra; it is a heartwarming portrait of friendship at its most durable and optimistic.